The present invention relates to steam generators and more specifically to an improved heat recovery steam generator (“HRSG”).
Heat recovery steam generators have been used to recover heat from various processes that result in high temperature exhaust gases. The hot exhaust gases are passed through the heat recovery steam generator, which has a variety of heat exchanging surfaces to further process the excess thermal energy contained in the exhaust gases. As exhaust gases pass through the heat recovery steam generator, the heat from the exhaust gases is transferred by the heat exchanging surfaces to fluid, such as water, passing through the system. The fluid absorbs the heat from the exhaust gases, and a portion of the fluid is converted into steam. The steam is then removed from the heat recovery steam generator and may be used to perform work in other processes. For example, the steam may be used to propel turbines, such as those used in electrical power production. Additionally, the heat recovery steam generator may have gas or oil-fired burners to further combust the exhaust gases. As a result, the amount of steam generated can be significantly increased, thereby maximizing the amount of work that can be performed.
As an example, a typical heat recovery steam generator includes a plurality of boiler tubes that serve as the heat exchanging surfaces within the device. Fluid such as water circulates through the boiler tubes. As the hot exhaust gases pass through the heat recovery steam generator, the heat from the exhaust gases is transferred through the boiler tubes and is absorbed by the fluid circulated within the tubes. A portion of the fluid is converted into steam, which is then removed from the heat recovery steam generator and used to perform work in other processes such as electrical power production.
Heat recovery steam generators have been used in tandem with various other devices that produce high temperature exhaust gases. For example, heat recovery steam generators may be used in tandem with gas turbines to further process the exhaust gases, thereby improving the overall efficiency and reducing the fuel requirements of the power production process. The exhaust gases exiting from gas turbines are extremely hot (typically 800° to 1000° F.) and oxygen rich (75 to 80 percent of that typically found in atmospheric air), meaning that they still possess recoverable thermal energy. In a time when the increasing demand for fossil fuels has driven the cost of natural gas to unprecedented levels, it is imperative that inefficiencies in power production be addressed and improved.
Heat recovery steam generators may be built on-site or factory-assembled and transported to the operating site. Heat recovery steam generators that are built on-site typically are custom designed for a specific function. On the other hand, prefabricated or “package” heat recovery steam generators, so-named because they are factory-assembled and transported to an operating site, are often designed for a wide variety of applications. As such, many conventional heat recovery steam generators are designed to maximize the flow capacity, which typically is accomplished by maximizing the size of the generator. Because most package heat recovery steam generators are shipped to the operating site via truck or rail, many conventional generators tend to be greatly oversized for most applications, thereby contributing to the inefficiency in the power production process.
Accordingly, there is a need in the art for a heat recovery steam generator that maximizes the flow capacity and efficiency of the generator. At the same time, there is a need in the art for a heat recovery steam generator that minimizes the size of the device to allow for convenient transportation. Although this invention is not limited to package heat recovery steam generators and is applicable to all types of heat recovery steam generators, it is particularly useful for package heat recovery steam generators and those designed for general purpose use.